Projectors are commonly used for giving presentations, such as in meetings and school classrooms, or for creating home theatre in users' homes. One example of a projector of the type described above is a projector that uses a high pressure discharge lamp as a light source. In recent years there has been demand to increase life of the high pressure discharge lamp, and also to reduce flickering that occurs when the high pressure discharge lamp is operated using eco-power, which is lower than a power rating of the high pressure discharge lamp (for example 50% to 80% of the power rating), in order to improve energy efficiency of the high pressure discharge lamp.
The high pressure discharge lamp includes an arc tube having a glass bulb with mercury and a halogen substance sealed therein, and having a pair of tungsten electrodes disposed in opposing positions to one another in the glass bulb. The high pressure discharge lamp emits light by generating an electrical discharge arc between the two electrodes. Electrons discharged by whichever of the electrodes is functioning as the cathode (referred to below as a cathode phase electrode) collide with whichever of the electrodes is functioning as the anode (referred to below as an anode phase electrode), thus causing temperature of the anode phase electrode to increase. In contrast, temperature of the cathode phase electrode decreases over time.
During lighting of the high pressure discharge lamp, tungsten evaporates from the anode phase electrode, and via a halogen cycle the tungsten deposits again on an end of the cathode phase electrode, thus forming a tip on the end of the cathode phase electrode. The above is a result of a tungsten halide compound dissociating in the halogen cycle to produce positively charged tungsten ions which are attracted towards the cathode phase electrode. The tip becomes an arc spot for the electrical discharge arc generated between the electrodes.
However, if surface temperature of the tip becomes excessively low, arc jumping occurs in which the arc spot for the electrical discharge arc on the surface of the tip changes, thus causing instability of the electrical discharge arc generated between the electrodes. If the electrical discharge arc becomes unstable as described above, flickering occurs in the high pressure discharge lamp.
In order to solve the above problem, one conventional art proposes a high pressure discharge lamp in which arc jumping on the surface of the cathode phase electrode is prevented by an absolute value of current flowing between the electrodes being increased directly prior to a polarity inversion of the current. The above causes increase in temperature of the anode phase electrode which becomes the cathode phase electrode after the polarity inversion. Therefore, surface temperature of the tip of whichever electrode becomes the cathode phase electrode after the polarity inversion is prevented from decreasing to an excessively low temperature during a period until a next polarity inversion of the current (refer to Patent Literature 1).